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80p or 100p or 120p?
#1
Hi all, just joined because HB's videos got me excited. I've been collecting and recycling 18650 cells for years, mostly for flashlights and small projects. Now I'm dreaming big! Are there any BIG advantages or disadvantages of going 80p vs 120p or 80p vs 100p? My space constraints would make 100p ideal for me.
Thanks!
Scott
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#2
It depends on what you have for batteries and what you are looking for in Ah/kWh output.

If your batteries are let's say average 2000mAh in an 80p pack then you would have 160 Ah which is ≈ .64kWh
with a 7s80p of that configuration it would be at 4V ≈ 4.48kWh
with a 14s80p it would be ≈ 8.96kWh

Now for the same 14s80p pack if your cells are 2600mAh in a 14s80p is ≈11.65kWh.

First you want to figure out what you want the pack to produce then you plan accordingly.

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#3
Between these options, I would optimize for space and future maintenance.    In my case, I'm nearing 86 packs.  Some are 130p and some are 102p because some are 1900mah cells and some are 2600mah cells...   different purchases over 3 years.   In my opinion - its hard to say "I'm going 80p exactly" as you don't know what deals on cells you may find over time.

I settled on 260ah (+/- 2%) per pack for my physical design.   So I need 260,000/1900 = 136cells for some packs and 260,000/2600 = 100cells for others.  On the 100cell packs, I just have empty slots in the base 4x5 cell holder design - but overall, the packs are interchangeable as far as capacity and physical deign.    So you can finalize the shelving or cabinet and still have flexibility for future packs / battery purchases.

I understand that you don't want to mix packs of different cell types in series - but this gives flexibility to distribute the different cell types evenly parallel wise and I do with good success.
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#4
It also depends on what "you" want to lift and move around when needed.
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#5
(05-21-2020, 07:26 PM)Korishan Wrote: It also depends on what "you" want to lift and move around when needed.
Excellent point!  If you use about 45g/cell * 100cells ~ 10lbs / pack.   A14s100p that's 140lbs per battery.   10lbs doesn't sound like much 'on paper' but try lifting it in place from an awkward angle etc...  its worth keeping in mind for your overall design.
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#6
Physical size, required capacity, discharge rate... more in parallel the more capacity and discharge potential you can have... but is it warranted against cost, size, weight.

It helps a lot to know what you want to power with it.

Then take into consideration that you can have different build methodologies that work better depending on scale.
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#7
As Long as the finished pack is able to handle the load and system without stressing the pack size doesnt matter much IF its bigger. Its just a physical issue.
Bigger packs though require beter bms that can balance .

So whatever 80, 120 or 200 go for what you got a d have. Exclude cells that are in the limit and rather build smaller packs.
Dont build any packs untill you got all cells so you dont have to scimp out on last packs. Thats One of the most Common failures out There to why you see People with issues
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#8
Thanks all! I'm going to ask some specific questions in a new thread.
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